TMNT - Monster I Have Become
by Roxina1000
Summary: When Donatello tries to create a retromutagen that will turn him into a human boy, it is the perfect idea. He can finally be with April. So what goes wrong?
1. Part 1

Donnie was in his lab, creating another batch of retromutagen. Potions and vials surrounded the turtle as he swirled a purple liquid around in a beaker, testing for acidity. It was the perfect idea.

This was the theory: If he mixed a certain type of DNA with the existing retromutagen formula, he could control what the user would de-mutate into. Initially, he could turn the user back to their existing form, or change them to their other form - in other words, he could change them into the creature that possessed the other DNA, rather than the original. Following this formula, Splinter would become a rat rather than a man, Rahzaar would become completely canine rather than human, and he, Donatello, would become a teenage boy. It was the perfect idea. He could finally be with April without worry of being outcast and rejected for his appearance. And maybe April would accept his new form more than the old one.

...So where did it all go wrong?

Donnie took a deep breath, filled a syringe with the purple liquid, and injected it into his arm, watching as the needle penetrated flesh and muscle, wincing slightly. He put the now empty syringe back on his desk. For a few silent moments, nothing happened. Donnie was beginning to wonder if he'd done something wrong when it happened.

A searing, burning pain broke out all over his body all over at once. He was paralysed. Donnie fell to the floor, crying out in pain, short spasms jerking through his body, forcing him to curl up in agony, groaning loudly. It was unbearable. Donnie's mind was racing. What was happening?!

Leo was watching the latest episode of Space Heroes when a pained cry cut through the air, breaking his focus on the screen. Leo recognised the voice. It was Donnie. "Donnie!" Leo was up instantly, running into the lab, wondering what on earth had happened. He looked around. The lab was chaos. Liquid was dripping from Donnie's desk and on to the floor, there was broken glass everywhere, and there was electrical wiring, ripped from its sockets, tangled around various bits of machinery. Donnie was nowhere to be seen. "Donnie?" Leo called out, half in worry, half in confusion.

A low, rumbling growl filled the lab, reverberating through the air, making Leo edgy and nervous. What was that? A pair of burning yellow eyes flashed open from the darkness of the ceiling above Leo's head. The blue-masked ninja didn't even hear it coming. One minute, he was standing there, and the next minute he was lying flat out on the floor with... well, with this thing on top of him.

The creature's skin was pale green and was marked with light mottling. It had long arms and legs, ending in wicked claws the length of throwing knives. it stared Leo down with those burning yellow eyes, it's pupils dark, foreboding slits which seemed to promise death to anyone who crossed its path. On its back, a gathering of jagged, rock-hard spikes running along its spine seemed to indicate a shell. It screamed into Leo's face, showing an impressive set of shark-like teeth, filed to needle-like points, serrated around the edges. A tail, long and ending in a crooked curve, jutted from its rear, lashing from side to side.

The creatures claws cut into Leo's shoulders and chest like a knife through butter, the red of his blood staining its hands. It snarled, pinning him to the floor, staring into his eyes. That was when Leo's noticed it. A piece of tattered purple fabric tangled around the creature's neck. It couldn't be. "...Donnie..." Leo's eyes widened. The creature seemed to recognise the name, and for a moment, it loosened it's grip, a mixture of anger and surprise etched into its features.

Leo took his chance. Pulling his legs free, he gathered his strength and kicked up at the creature, throwing it off forcefully. It was hurled towards the far wall, screeching its rage at Leo. It hit the wall back-first, slamming into the cold stone, before falling to the floor, dropping out of sight behind the Shellraiser. There was another screech - this time of pain - then a softer moan, and finally silence. Leo stood slowly, his legs trembling, his head too pumped full of adrenaline to notice the blood running from deep slash marks on his shoulders and thighs.

A few moments passed. Then, a small, scared voice called out, the sound barely audible. "...L-Leo?" Just before he heard his name, Leo looked down, realising the blood loss to his system. Slowly, almost painfully, he crumpled to the floor, out cold.

Donnie walked out from behind the Shellraiser, shaking badly himself. He felt a deep, aching pain as if he'd just woken up after going on a 30 mile hike the day before. He stumbled, rather than ran, over the Leo as soon as he saw his brother lying on the floor, a pool of his own blood collecting around him. "Leo!" Donnie was shocked. "Speak to me, Leo!" Nothing. His hands felt wet. He looked down.

Donatello couldn't have possibly comprehended what had happened. It could have been a thousand things. But looking down at his own hands, stained red and dripping with Leo's blood, he knew. It wasn't possible, but he knew.

"...I did this."


	2. Part 2

Mikey and Raph could hear screeching. At first, they ignored it. But as it became louder, and they realised that Leo had left halfway through an episode of Space Heroes, they came to the conclusion that something was wrong. The two ran into the lab, and for once, they were both speechless.

Leo was lying on the floor, bleeding badly and looking deathly pale. Donnie was kneeling beside him, his head bowed, his hands covered in his brother's blood. Raph was first to speak. "Donnie, you didn't..." Mikey pitched in. "D, what happened? Say something, bro!" Donnie got up slowly, still staring down at Leo, before lifting his gaze to his two other brothers. Silently, with shocked eyes, he shook his head, backing away. Then, he turned, and ran.

Raph and Mikey did nothing to stop him.

Donnie didn't stop running until he got to the first place he could think of - April's apartment. He banged on the fire escape door, not stopping until April opened it, looking out at him bleary-eyed. The red-head rubbed sleep from her eyes and yawned. "Donnie? whaa...?" April looked up at the ninja's face, not used to seeing him without his mask, realising that the familiar piece of fabric was now around his neck, in shreds. Glancing down, the sight of blood caused her to snap awake suddenly. "Donnie, are you hurt? Come in!" She ushered him inside, closing the door for him as he sat with his back against the wall, hyperventilating quietly. April walked over, kneeling in front of him. "Donnie, what happened?"

"L-Leo... I h-hurt Leo.." he managed, staring straight ahead, looking straight through April as if she wasn't there. "You hurt him?!" April was shocked. She knew Donnie well, and he wasn't the kind to lash out at anyone, let alone to the point of causing any serious injury. She frowned, but stood and walked over to her bedroom door. "I'll go for some water. We'll get you cleaned up." She comforted, before walking out and closing the door softly behind her.

Donnie just sat there, his hands trembling. He couldn't stop replaying the last half hour over in his head. The potion. The pain. Leo. The blood running down his arms. He closed his eyes, his voice cracking, on the verge of tears. "What... what have I done...?" He stood and went over to a mirror on the wall.

One of his eyes was bright yellow.

The pain came rushing back. Once again, Donnie found himself curled on the floor in agony. "H-help me! Somebody!" He wailed, his back to the door, trying to stand but only getting halfway. April rushed it, but when she saw Donnie, she dropped the bowl of water she was carrying. the liquid spilling out and the glass smashing on the floor. She watched as his shell grew jagged and spiky, his body slowly morphing into something altogether more sinister. "Donnie!" She took a step forwards, wanting to help but not knowing how.

"Stay away from me! I'm dangerous!" Donnie shouted, his voice warped and rough, nothing like his usual tone. He was clutching at his head, crying in pain, half standing, half kneeling. April was across the room in two short strides, placing a hand on his arm. The skin was cold to the touch. "Donnie, calm down!"

"I said, stay AWAY!" Donnie turned around, throwing April off with more force than should have been possible. He went still, suddenly silent. April landed a few feet away, scrambling to her feet, a look of confusion and fright on her face. "...Donnie?" she questioned. And slowly, he turned to face her.

April's sky blue eyes were met with acid yellow, the slitted pupils darting around maniacally as if trying to escape the burning yellow pools that encased them. There was not a shred of humanity in those features, just pure, raw hatred for everything that surrounded them. The creature, or to be more precise, Donatello, crossed the room with surprising speed. April found herself against the wall, with her feet off the ground and a cold, steely grip around her neck. Donnie stared into her eyes just like he'd done with Leo. April was choking, struggling to ease his grip on her throat. He snarled, once again revealing those wicked teeth, his face centimetres from hers. "D-Donnie! It's me, A-April!" she said, barely a whisper. Donnie's features relaxed slightly, along with his grip. He spoke. "...Ap..rilll?" his voice was deep and gravelly, the name ending in a snarl as if he hated that, too. April was gasping for breath. "Yes, i-it's me! You wouldn't h-hurt April, w-would you?" It was a challenge. April managed to bring her gaze around and lock eyes with Donnie. Donnie gave a low, rumbling growl, and let April go. She breathed in, relieved to not have claws around her neck any longer.

Donnie backed away, his animal brain confused. Why didn't he feel the urge to kill this girl? He'd felt the need to kill the other one, the one that mocked his appearance, the one with the blue mask. So why not her? It was almost beyond him, but he even felt protective of her. Confused and alone, he turned and leapt, smashing through the fire escape door. At the last moment, the mask, still tangled around his neck, caught on the door hinge, half-strangling him, pulling him back. He screeched his rage and slashed at the material, cutting himself free and disappearing into the night.

April walked to the fire escape, not taking her eyes off the spot where Donnie had stood. Silently, she reached out a hand and pulled the ragged remains of his mask from the doorframe, and sat down, hugging it close to her heart, tears trickling silently down her cheeks.


	3. Part 3

(Message to all you guys :)

D0ntE770: Woah, calm down! XD Sorry I haven't updated recently, Iv'e been super busy and honestly I'm still not 100% good at using Fanfiction to post my stories :P This is part three, the next part will be the final part :)

And thank you all for your reviews :D)

It was strange, building your own prison. Donnie had returned to the lab after he woke up behind a trash skip, covered in blood that didn't belong to him. He felt sick. Leo was recovering from the day before, walking already, although shakily. The slashes on his upper body would scar, Splinter had said. Leo and Donnie had decided to keep the whole thing a secret, blaming Leo's injuries on a lab accident. Mikey and Raph had their suspicions, but they didn't know enough to go pointing fingers, and kept their mouths shut.

Donnie's shaking hands held up the screwdriver as her bolted the last side into place.

The cage was made of solid steel, bolted to the floor. The door had a heavy-duty lock on it and Donnie had created an electrical force field which would activate if the bars were put under too much pressure from the inside, electrocuting the inhabitant. The worst part was, the inhabitant was going to be him. But first, he had to go and apologise to April.

Minutes after the cage construction was complete, Donnie was at April's knocking on the fire escape door. The redhead walked over, tear stains still darkening her cheeks. "Donnie." April didn't seem to be able to say anything else. "A-April... I... I just wanted to say.. I am so, so sorry for what happened last night. I don't e-expect you to forgive me. Just... Just know I would never hurt you intentionally. Until I can stop these... Mutations, I think it's best if I stay away from you." Tears blurred his vision, but he blinked them back, determined to keep a straight face. April didn't reply. Donnie took one last look at that face, that beautiful face framed by streaks of red hair, before turning, and walking away. It was possibly the hardest thing he'd done in his life. But April called out to him. "Donnie, wait!" She ran to him, and flung her arms around him, tears flowing freely. "We can do this. My dad, he-he'll find a cure for you. I'll never give up on you."

Despite himself, Donnie gave April a small smile. "Thanks, April." The redhead looked up, her eyes shining up at him. "Donnie, you've got to promise me something. Never give up. "

"April, I-"

"Promise?"

And looking down at her, staring up at him with fierceness and grief and love in her eyes, Donnie couldn't say no. He nodded, and she let him go, stepping back. "See you around then?" She laughed shakily. Donnie made a small sound of amusement. "Yeah, see you around."

And with that, he was gone.

Back at the lair, Donnie silently watched as Leo locked the door on his cage. His older brother locked eyes with him. "Don.. I.."

"Leo, it's not your fault. There was nothing you could have done. Shouganai." This last phrase was something they used frequently in Japan, simply meaning 'It can't be helped'. Leo looked down, turning away. Just then, Master Splinter walked in. He looked at Leo, then at Donnie who at sat down, his back against the bars. "Leonardo, what is the meaning of this?" He demanded, Splinter went over to unlock the door of the cage, but Leo intercepted him. "No, Master Splinter! He's dangerous!"

"Leonardo! I would have thought you would be more respectful to your brother! Release him immediately!"

"Please, Sensei!" Donnie spoke up, his voice cracking. "Don't make this harder for me than it already is." Master Splinter gave him a look. Donnie sighed. "It... It was the retromutagen. I thought if I altered the recipe, I could alter the genetical structure of the recipient- um, I could turn fully human, so I..." He trailed off.

"Yes?"

"...So I could be with April. But something happened, I don't know what. And now I.. I... Argh!" Donnie clutched at his head in pain. The cry had brought Mikey and Raph running into the room. Leo turned away, not wanting to watch the horrifying transformation. Master Splinter's voice was dripping with worry. "Donatello!"

"Shouganai!" Leo shouted over Donnie's screams, trying to calm the old rat down. "We need another scientist, someone who can cure him."

Leo and Raph spoke at the same time. "Mr. O'Neil!"

At April's apartment, her phone began to ring, the words 'Ichiban Turtle' flashing up on the screen in green lettering. Quickly, she answered the call. The noise on the end of the phone was a chaos of sounds, crashes and screeching followed by "April! We need your dad over here right now!" That was enough. April dropped her phone onto the bed and ran into her dad's office. "Dad!"

Kirby O'Neil turned, the panic in his daughter's voice raising his concern. "April! What's wrong?"

"It's Donnie! He's in trouble!"

Kirby nodded his understanding.

Ten minutes later, the two were in the lair, with Kirby at Donnie's desk, pouring liquid into a beaker. Donnie stood at the back of the cage, screeching at anyone who got too close. Occasionally, he would bash at the bars with his fists, only causing blue streaks of electricity to run across his arms, crackling as they bit into him like so many writhing snakes. He hissed in pain, recoiling for a moment, before lashing out again, screaming his frustration. April blinked back tears, hating to see her best friend in such a state.

Mr. O'Neil reached under Donnie's desk for another canister of mutagen to add to the mixture, but his fingers only brushed against empty air. "We're out of mutagen! We still need six more canisters."

Leo frowned. "We don't have time to search for more in the streets. Besides, we need Donnie to track it. Well have to raid a Kraang warehouse."

Mikey piped in. "What about that place where they mutated Timothy? The explosion wouldn't have damaged the mutagen crates much, they were made of steel." Everyone turned and stared at the young turtle in surprise. "That's... Actually a really good idea." Raph was the first to admit. "Where did you learn about the resistant qualities of metal?" Kirby asked. Mikey shrugged. "Donnie taught me. I don't think he thought I was listening." Mikey looked somewhat sadly over at Donnie. "I never got to tell him how much I've actually learnt from him."

April's head raised from where she'd been staring dejectedly at the ground. "Don't talk about him like he'll never be himself again! We'll save him!" She snapped.

Mikey was taken aback by April's harsh tone. He blinked. "...sorry." April apologised. "I'm just so worried for him, that's all." Leo put a comforting hand on her shoulder. "We're all worried about him. Come on, guys, let's go get that mutagen. We'll be back." Leo, Raph, and Mikey all turned to leave. April stopped them. "I'm coming too."

"No way, it's too dangerous for you. Who knows how many Kraang droids will be guarding that place?"

April gave Leo a look which said: 'I'm coming whether you like it or not, deal with it'. Leo sighed. "Fine, then. Let's go.


End file.
